The present invention relates to a hybrid vehicle. More specifically, the present invention relates to a method and apparatus to provide a smooth transition between an electrical traction motor and internal combustion engine in a hybrid vehicle equipped with an automatic transmission.
In today""s automotive market, there exist a variety of propulsion or drive technologies used to power vehicles. The technologies include internal combustion engines (ICEs), electric drive systems utilizing batteries and/or fuel cells as an energy source, and hybrid systems utilizing a combination of internal combustion engines and electric drive systems. The propulsion systems each have specific technological, financial, and performance advantages and disadvantages, depending on the state of energy prices, energy infrastructure developments, environmental laws, and government incentives.
The increasing demand to improve fuel economy and reduce emissions in present vehicles has led to the development of advanced hybrid vehicles. Hybrid vehicles are classified as vehicles having at least two separate power sources, typically an internal combustion engine and an electric traction motor. Hybrid vehicles, as compared to standard vehicles driven by an ICE, can have improved fuel economy and reduced emissions. During varying driving conditions, hybrid vehicles will alternate between separate power sources, depending on the most efficient manner of operation of each power source. For example, a hybrid vehicle equipped with an ICE and an electric motor will shut down the ICE during a stopped or idle condition, allowing the electric motor to propel the vehicle and eventually restart the ICE, improving fuel economy for the hybrid vehicle.
Hybrid vehicles are broadly classified into series or parallel drivetrains, depending upon the configuration of the drivetrains. In a series drivetrain utilizing an ICE and an electric traction motor, only the electric motor drives the wheels of a vehicle. The ICE converts a fuel source to mechanical energy to turn a generator which converts the mechanical energy to electrical energy to drive the electric motor. In a parallel hybrid drivetrain system, two power sources such as an ICE and an electric traction motor operate in parallel to propel a vehicle. Generally, a hybrid vehicle having a parallel drivetrain combines the power and range advantages of a conventional ICE with the efficiency and electrical regeneration capability of an electric motor to increase fuel economy and lower emissions, as compared with a traditional ICE vehicle.
The present invention includes a vehicle having a parallel hybrid drive system incorporating an internal combustion engine (ICE), a conventional multi-speed automatic transmission and an electric motor generator (MoGen). The MoGen provides for propulsion of the vehicle during certain vehicle operating conditions, replaces an alternator to charge a battery pack in the vehicle, and replaces a conventional starter motor to start the ICE. The hybrid drive system of the present invention will utilize the ICE and MoGen to propel or motor the vehicle during the vehicle conditions which are most efficient for the ICE or MoGen operation. For example, during coasting, deceleration, and/or a stopped condition, fuel flow to the ICE will be cut off, as these conditions are some of the least efficient conditions to run the ICE. A fuel cut-off can be initiated by the application of a brake pedal, the release of a gas pedal or other similar indicators of a deceleration condition in the vehicle. The fuel cut-off function includes shutting off fuel, one cylinder at a time, to provide a smooth deceleration feel. Just before the cylinders are being shut off, an idle air control (IAC) motor or electronic throttle and the MoGen may be conditioned to help smooth the torque at the crankshaft of the ICE.
The MoGen system becomes the active propulsion or motoring system during this fuel cut-off feature and powers the vehicle without noticeably disturbing the operation of the vehicle or sacrificing driveability. The MoGen will propel the vehicle and smoothly transition the vehicle from the idle or stopped state and start the ICE for ICE driving conditions. The transfer of power between the MoGen and ICE, or vice versa, coupled to an automatic transmission should be transparent to the operator.
During normal operation of the vehicle when the ICE is running, the MoGen will act as an electrical generator to supply electrical power to the vehicle""s electrical infrastructure (fans, radios, instrumentation, control, etc.) as well as recharging the battery pack. The battery pack and a power supply, such as a DC-DC converter, will supply power to the vehicle electrical infrastructure and power the MoGen when it is operating as the motoring device for the vehicle. In the motoring mode, the MoGen is an electrical load drawing current from the battery pack.
The control of the ICE and MoGen is executed using software routines that operate in conjunction with the normal operation of traditional powertrain and automatic transmission systems for powering a vehicle. In traditional powertrain systems during an ICE startup mode, the ICE is first driven by an electric motor starter and then supplied with fuel and spark. The automatic transmission is placed in a drive mode and the vehicle is accelerated by depressing an accelerator pedal for supplying more air and fuel to the ICE. When the vehicle is up to speed, a torque converter lock-up clutch in the automatic transmission is applied and the transmission is in a forward speed selection position such that the vehicle cruises under the power of the ICE.
When a conventional vehicle ICE is not running (0 rpm), the automatic transmission is not energized or primed [i.e., not ready to carry torque, as the transmission""s clutch pack (e.g., for first gear) is not energized] because the transmission oil pump is not spinning. This situation will also occur when the transmission is either in the P (xe2x80x9cParkxe2x80x9d) or N (xe2x80x9cNeutralxe2x80x9d) position.
An electric starter is normally used to crank the engine crankshaft to a certain speed before spark and fuel are commanded to produce combustion (i.e., torque). To stabilize combustion, the IAC motor or electronic throttle is utilized to achieve the desired engine torque and speed. Once the transmission is shifted into the D (xe2x80x9cDrivexe2x80x9d) position, a garage shift is performed to energize the transmission gear allowing the ICE to transfer torque to the wheels. As each event in this sequence occurs, a corresponding torque disturbance multiplication arises creating a decrease in the driveability of the vehicle. If a hybrid powertrain were to undergo this sequence after each fuel shut-off and start of the ICE, the driveability of the hybrid vehicle would be unacceptable.
The present invention incorporates a system and apparatus that controls the torque output of a hybrid powertrain system having a conventional automatic transmission to enable the hybrid vehicle to start and respond smoothly, emulating a conventional ICE powertrain.